GPO 746 bell tinkle problem

[twocvbloke]

The 3.3k resistor in series with a 1000 Ohm ringer coil (or coils) is to reduce the REN from 4 to about 1, to reduce the load on the line and to give the subscriber the use of more phones, as the average UK phoneline, at least back in the day, could supply up to about 4 REN in current...

And yes, the bells should indeed be adjusted so the clapper doesn't touch the bells, with at least a 1 to 2mm air gap between the edge of the gong and the clapper hammer, that way it's louder and reduced the random tinkle when using other phones...

As for the PSTN thing, well, that's what I'd been told it was by a former GPO/BT guy, but then he was the sort to wire up 100 pairs in a frame only to realise he'd not passed the bundle through the panel grommets...

[Jack Ryan]

The 3.3k resistor in series with a 1000 Ohm ringer coil (or coils) is to reduce the REN from 4 to about 1, to reduce the load on the line and to give the subscriber the use of more phones, as the average UK phoneline, at least back in the day, could supply up to about 4 REN in current...

That is the purpose but as a side effect, it will also mitigate bell tinkle (albeit with reduced ring intensity).

As for the PSTN thing, well, that's what I'd been told it was by a former GPO/BT guy, but then he was the sort to wire up 100 pairs in a frame only to realise he'd not passed the bundle through the panel grommets...

Sounds like you had better review any other gems he has passed on ;-)

Regards
Jack

[twocvbloke]

Sounds like you had better review any other gems he has passed on ;-)

Not many to be honest, the only ones that comes to mind was him and his co-workers testing DTMF systems by making tunes with the tone generators they used, and working on the remaining mechanical switches was a filthy job due to him over-oiling everything making the switchbanks sticky and dirt-absorbing (and thus breakdown-prone), other than that there's not much, he seemed to resent the job as he was given the heave-ho "for some reason" in the post-selloff BT era , never did say why though...

[Jack Ryan]

he was given the heave-ho "for some reason" in the post-selloff BT era , never did say why though...

Can't think of a single reason...

Season's greetings.

Regards,
Jack

[twocvbloke]

Can't think of a single reason...

I have a feeling it was something a bit "seedy" that got him the sack, but I'm not going to go into that, cos it's only alleged... 

[andy1702]

I probably will redo the wiring with a new faceplate as mentioned though in the new year, and run the ADSL on a separate pair of wires (within the same cable). Just need to replace a short stretch of wire between the master and first extension because it is only 2 pair. The rest of the cabling round the house is 3 pair so won't need to redo that thankfully.

Thanks again,
Barry.

You can split the ADSL at the faceplate if you like, but those new master faceplate splitters are a bit difficult to find sometimes. That's one of the reasons I sent the combined signal up a single pair, split it at a standard extension socket in the computer room using a normal ADSL filter, then sent the split telephone signal back down a second pair in the same cable to the front room and fitted a second socket there to plug a phone into. There's no phone in the original master, which I basically just use as a junction box. This negates the need to find the fancy faceplate.

Regarding the 746 phones, I'm a bit surprised you can only get two good ones out of four. I have lots of them and I've never needed to canibalize one for spares. They're so rugged it's normally a case of having to adjust things rather than needing to replace anything.

Andy.

[royalbox]

Hello Andy,
Thanks for the info, not sure how far I want to go with the rewiring, really I'd like to get it under the floorboards from room to room but that's a big job. I don't like cables going round doors or under carpet really, just fussy I suppose.

As for the 4 phones, I'm just swapping the best looking parts (dials, dial faceplates, cases, cables etc) to make up 2 really nice ones to keep and sell the other 2 later on. They will all still work don't worry.

Thanks again,
Barry.

[andy1702]

I run the cables around the outside of the house where possible. Other places it runs along between the skirting board and the carpet. It almost disappears when it's tucked down there. Another clever product I've seen is a skirting board that's actually a cleverly disguised cable duct. you nail the main part to the wall like ordinary skirting board, run your cables along in a built in recess, then clip a plastic cover over the top. I thought that was good because you don't damage the cables with clips and it's easy to access for repairs or adding extra cable capacity at a later date. You could probably even run electric cables down there and easily fit extra power sockets around the room. It's stocked at the giant B&Qs.

If you're swapping phone bits over, could you please do me a favour and make a note of what you've removed/added and stick it inside the phone cases? I always try to correctly restore everything to how it would have been at some point in it's working life. You won't find any pink cases or 746s with coloured finger wheels around here!  The problem is you'd be amazed how much information has already been totally lost. A good example of this is the alpha-numeric dial bezels on 746 phones. There are well known people in the phone collecting field who swear these lettered bezels were only fitted to 706s, not 746s and for ages I believed them. Then I just happened to find an old film with a very brief shot of a 746 with the lettered dial bezel dating from 1970. So I scoured E-Bay until a 746 with a lettered bezel turned up. I've seen these before but assumed them to have been messed with. Luckily this one was filthy dirty and you could tell it hadn't been apart for years. When checking the moulding marks in the plastic parts they all matched. So I can now say some (but maybe not all) 706s produced between 1967-1970 definitely did have alpha-numeric dial bezels. Of course the more parts get mixed up, the harder this type of detective work becomes. So when swapping parts I try to encourage everyone to document what they've done and stick the details up inside the case for the next owner to discover 40 years later. Wouldn't it be good if every phone we took the cover off had one of these little time capsules?

Andy.

[royalbox]

Thanks Andy, will look in the new year regarding wiring. Want to keep the wiring inside though.

I bought an unrestored green 746 a few months ago off eBay. The seller never mentioned the crack in the case at the front, nor the broken tab off the bezel surround, nor the missing retaining nut at the back, or the piece broken off the dial wheel, or the broken plastic dust cover at the rear of the dial. Couldn't tell any of this from the photos, I always ask first now.

I bought another green one recently, very dirty with some rust here and there but with an intact case. I just used the best looking and least scratched/marked/broken parts from both to make a nice one. Both will remain as standard.

Also have 2 ivory ones, one that hadn't been returned to BT (no red sticker or the like on the bottom) and has the old style sloping 746 case which I prefer the look of actually. Kept that one as it was and just changed the handset cable and did the "oxy-clean" treatment to remove the yellowing which was quite bad and patchy. Came out well after polishing.

Had to buy a replacement dial for the other as it had the cheaper all-plastic dial (No. 54 from memory) and the little plastic piece that holds the centre of the spring in place broke off and made the whole thing useless. I bought a type 21 dial that had the plastic trigger, centre screw and finger stop missing. Made a good one out of the 2 but need to get screws for the finger stop.

The only other thing I did was replace the transmitters on the 2 that had carbon types with electronic ones as they had the noisy "bacon frying" effect that people talk about.

Barry.

[twocvbloke]

It's stocked at the giant B&Qs.

Do they still exist? The one in Durham (easiest one for me to get to) went from being a huge store to being shrunk by two thirds into a tiny little one, resulting in it suddenly feeling like a wasted effort of a store, almost as if they were close to shutting it permanently... 

[andy1702]

The only other thing I did was replace the transmitters on the 2 that had carbon types with electronic ones as they had the noisy "bacon frying" effect that people talk about.

Barry.

It's strange, but I've never noticed any need to replace a transmitter in a phone. I've got quite a few 706s and a few earlier bakelites and they all seem fine. Maybe I just got amazingly lucky? The beauty of having a PBX is I can call one phone from another so I can hear what's being transmitted.

Andy.

[andy1702]

Do they still exist? The one in Durham (easiest one for me to get to) went from being a huge store to being shrunk by two thirds into a tiny little one, resulting in it suddenly feeling like a wasted effort of a store, almost as if they were close to shutting it permanently... 

Plenty of B&Qs here in North Derbyshire / South Yorkshire area. It's best to find a REALLY big one though if you want something obscure (like a nut and a bolt!)

Andy.

[twocvbloke]

It's best to find a REALLY big one though

Which the one in Durham used to be, but is now a Micro Block & Quayle... 

[andy1702]

Also have 2 ivory ones, one that hadn't been returned to BT (no red sticker or the like on the bottom) and has the old style sloping 746 case which I prefer the look of actually. Kept that one as it was and just changed the handset cable and did the "oxy-clean" treatment to remove the yellowing which was quite bad and patchy. Came out well after polishing.

Barry.

What exactly did you use for the "oxy-clean" Barry? I've seen various suggestions, but most are for American products. I tried some Tesco stain remover which seemed to have some of the correct ingredients, but it didn't seem to do much. Any chance of a photo of the results you got?

Andy.

[twocvbloke]

I've seen Vanish Gold Oxi-Action being used for an oxygenating cleaner, or a generic store-brand of something similar...